(1) Field of the Invention
The present invention relates to fans, pumps and propellers. More specifically, the invention provides methods and devices that utilize a caudal cycle to move gas or liquid from one location to another or that propel a craft through gas such as air or liquid such as water.
(2) Description of Related Art
Many marine fishes and mammals move through the water by the motion of their fins in a caudal cycle. This cycle has been harnessed by a variety of devices to move liquids and gases but none of these inventions come close to matching or exceeding the performance and efficiency demonstrated in nature.
The caudal cycle describes the movement of a propulsive surface, such as a caudal fin, so that it maximizes forward thrust while minimizing reverse thrust and drag. Two commonly recognized cycle types are the natural caudal cycle and the mechanical caudal cycle. Marine mammals and some fish use their caudal fin to perform the natural caudal cycle for propulsion. This is very different from other fins used for hovering or precision movement similar to the oscillations of the pectoral fins or the flexions of the dorsal fin used for steering, counter thrusting and twisting. The natural caudal fin in a marine environment has evolved to be highly reformable to suit the mammal or fish's needs under different conditions and is used to sense pressure variations, turbulence, speed and power loading. The fin can frequently become thinner and change its chord section to conform to reduce vortices coming from its trailing edge. The natural caudal cycle is driven by the leading edge and the blade component is mostly rigid and the trailing edge is positioned by the leading edge/tail pivot joint. To avoid undue turbulence the natural cycle is predominantly a pushing operation.
In the natural caudal cycle, the leading edge is oscillated from one side of the cycle extreme to the other relative to the speed of the water flow. The fin is then pivoted following the leading edge towards its direction of travel, pushing the water aft and the fish forward. This cycle is repeated with shallower cycles as speed increases.
The mechanical cycle is essentially the same as the natural caudal cycle, but has a longer thrust and coarse angle of attack at slow speed and a shallower thrust and angle of attack at high speed. In the mechanical caudal cycle, the leading edge is positioned toward the extreme off center of cycle, with the blade forming an ideal angle of attack for the blade. Maintaining this angle of attack the blade is thrust as far as it will go in that direction. The leading edge is stopped while the trailing edge is thrust to a position following the leading edge and parallel to the flow of the fluid. The leading edge is positioned toward the other extreme side of the cycle forming an ideal angle of attack for the blade. Maintaining this angle of attack the blade is thrust as far as it will go in that direction. The leading edge is stopped while the trailing edge is thrust to a position following the leading edge and parallel to the flow of the fluid. This cycle is then repeated.
U.S. Pat. No. 5,054,376 to Sanchez discloses a mechanical version of the natural caudal cycle used for moving air. However, the undriven trailing edge and non-rigid blade limits the force that can be directed toward driving the air and most of the blade surface provides only drag into the stream.
U.S. Pat. No. 5,401,196 to Triantafyllou et al. discloses an example of the mechanical caudal cycle in a ship-propelling device. However, this system is complex and has many parts susceptible to failure and its performance is limited compared to traditional propellers and their equivalents.
Therefore, there is a need in the field of fluid motion for an improved caudal cycle that can deliver better performance and reliability.